Vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, to block the flow of blood through a vessel or an aneurysm stemming from the vessel. Virtually all such vaso-occlusive implants are delivered by pushing the devices through wire-guided catheters.
One widely used vaso-occlusive device is a helical wire coil having windings that may be dimensioned to engage the walls of an aneurysm. For example, a vaso-occlusive device such as a helical wire coil may be positioned within the aneurysm space to cause or accelerate the formation of a clot and later-formed collagenous mass. The resulting occlusion fills and seals the aneurysm, thereby preventing the weakened wall of the aneurysm from being exposed to the oscillating blood pressure of the open vascular lumen. The use of vaso-occlusive coils for the treatment of aneurysms is a significant improvement over alternative surgical methods.
One common vaso-occlusive device is formed from a generally soft, helically wound coil. The coil may be formed by winding a wire (e.g., a platinum wire) about a primary mandrel and applying a heat treatment to impart a primary winding coil shape. The relative stiffness of the coil will depend on, among other factors, the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. As an example of an early vaso-occlusive device, U.S. Pat. No. 4,994,069, describes a vaso-occlusive coil that assumes a primary, linear helical configuration when stretched and a folded, and a secondary, convoluted configuration when relaxed in a minimal energy configuration. The coil assumes the stretched condition during delivery of the coil at the desired site by passage through the catheter, and assumes the relaxed configuration, which is better suited to occlude the aneurysm, once the device is deployed.
There are a variety of ways of discharging vaso-occlusive coils into the human vasculature. In some devices, vaso-occlusive coils are deployed from a delivery wire using a mechanical detachment mechanism. For instance, U.S. Pat. No. 5,234,437 illustrates a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. Alternatively, U.S. Pat. No. 5,250,071 shows an embolic coil assembly that uses interlocking clasps mounted on the pusher and on the embolic coil. In still another design, U.S. Pat. No. 5,261,916 shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. U.S. Pat. No. 5,304,195 shows a pusher-vaso-occlusive coiled assembly having an affixed, proximally extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengage when expelled from the distal tip of the delivery catheter.
Still other vaso-occlusive coils utilize an electrolytically-severable joint to release vaso-occlusive coils at the site of interest. For example, U.S. Pat. Nos. 5,354,295 and 5,122,136 disclose a device that uses an electrolytically-severable joint to place a finely wound platinum coil into a vascular cavity such as an aneurysm. The coil is delivered endovascularly using a delivery member such as a delivery catheter. After placement in the aneurysm, the coil is severed from a proximally located insertion core wire by the application of a small electric current to the core wire. The joint connecting the coil to the core wire is then electrolytically degraded to release the vaso-occlusive coil within the aneurysm.
While a variety of detachment modalities exist for vaso-occlusive members, there is a continuing need in the art for alternative detachment mechanisms.